Serna comes with the English word-list only. However, you can add Aspell dictionaries of your choice. A number of them are available at the Aspell website. To add a new dictionary:
Install Aspell on your system. Make sure that your system Aspell version is compatible with version 0.50.3. Note that Aspell of an earlier version will not work.
Download the new Aspell dictionary.
Build the new dictionary (see README that accompanies the dictionary package). Usually you need to input two commands in the package directory:
./configure make
Copy all the files *.rws, *.multi, *.alias to sernaInstallationPath/plugins/speller/dict. Make sure that files have correct read permissions.
Copy all the files *.dat to sernaInstallationPath/plugins/speller/data. Make sure that files have correct read permissions.